Electrodynamic reciprocation apparatus



June 1952 P. c. EFROMSON ETAL ,036

ELECTRODYNAMIC REC IP RQCATION APPARATUS I Filed Dec. 14, 1950 3 Sheets-Sheet 1 J ajj'mmiv 7 11 0682! 6. Lewis dizzy/s 6 1952 P. c. EFROMSON ETAL 2,599,036

ELECTRODYNAMIC RECIPROCATION APPARATUS Filed Dec. 14, 1950 3 Sheets-Sheet 2 Jkuezztori 1 /5/1 17)? afiymima'am flafieri 6'. 5620019 M 6.44...." W

J 1952 P. c. EFROMSON ETAL 2,599,036

ELECTRODYNAMIC RECIPROCATION APPARATUS Filed Dec. 14, 19 50 3 Sheets-Sheet 5 fmz'eizzari B/Zz'lg'o 6510mm B0607! 6.5620019 /W, WW

Patented June 3, 1952 vELEGTRODYNAMIC RECIPROCATION APPARATUS Philip C. Efromson and Robert C. Lewis, Winchester, Mass, assignors to The Calidyne Company, Winchester, Mass, at copartnership Application December 14, 1950, Serial No. 200,861

15 Claims.

This invention relatestovibration generators such as are used for sonic and under water sound vibration, processing, vibration testing and other similar purposes where reciprocating forces are required.

As manufactured heretofore, such generators or shakers generally have comprised a core. structure magnetized by a winding energized from a direct current supply so that a high flux concentration exists across an air gap in the structure. An armature coil is positioned within the air gap and energized from a source of alternating currentthereby to impart a reciprocating movement to an attached armature assembly. To'prevent other than a substantially axial movement of the armature assembly, it is usual to support the assembly by means of a spiral spring or a pair of nexures, the opposite ends of which are in either case rigidly attached to the armature assembly and core structure, respectively. The flexures are located upon the opposite sides of the core structure one of the flexurcs being connected to the assembly adjacent the armature coil, the connection between the other flexure and the assembly being made to one end of a rod or rods which passes through a centrically located aperture in the core structure so that the opposite end of the rod attaches to the bottom of a test table or bed located adjacent the armature coil. This mounting arrangement for the armature assembly gives satisfactory results in small shakers, but in large high power units it has been found that when the table and column are made rigid enough to withstand the resulting bending moments, their mass becomes so great that the acceleration of the armature assembly is limited. Another disadvantage of this construction is that, to shield the auxiliary signal generator from the effects of the leakage of flux from the air gap, it is necessary to mount the generator at the end of the column upon the opposite side of the coil structure from the armature coil, in which position the generator measures the velocity of such column end rather than the velocity of the table adjacent the mounting are minimized. Further objects are to position both the test table and signal generator where they are shielded from the air gap leakage flux, to mount the moving element of the signal generator so that it measures the velocity of th'e test table direcuyand to provide flexures 2 which are uniformly stressed and are not: sub.- jected to fatigue and which are attached to the armature structure in a novel manner.

In abroad aspect the invention contemplates a vibrationgenerator comprising a core structure which is preferably essentially E-shaped with a cylindrical air gap wherein a high flux concentration is produced by means of a field coilenergized. from a direct current supply. The generator armature assembly comprises a coil located in the air gap and a test table which is positioned upon the'opposite end of the core structure where it is shielded from the leakage flux adjacent the air gap. The table and coil are interconnected by a plurality of elongated connecting members or columns which extend through respective apertures in the core structure and which are preferably although not necessarily equally spaced about the periphery of the table.

In a more specific aspect the ends of the respective connecting members are provided with axially disposed slots for receiving a cylindrical member or barrel which acts as a spacer for maintaining the relative spaced positions of the connecting members. The armature coil is secured either by clamping it in the slots beneath the barrel or by securing to the extending end of the barrel in a plurality of encircling straps.

The armature assembly is constrained to move axially without substantial lateral movement, which would tend to bring it into contact with the adjacent core structure by means of a respective pair of fiexures or leaf springs located adjacent either end of the core structure so that the respective flexures extend between the structure and the armature assembly. Preferably the connections between the armature assembly and the respective flexures are made pivotal, the ends of the pair of flexures adjacent the air gap attaching to the end ring of the armature coil and the ends of the opposite pair of flexures attaching the assembly adjacent to the test table. The opposite ends of the respective flexures are rigidly attached to bosses extending from the core structure so that each .fiexure acts as a cantilever; By making the fiexure thickness in the direction of the axial movement of the armature assembly small with respect to the width of the flexures in a direction transverse to such movement, and by gradually decreasing the transverse width of each fiexure from a maximum width adjacent the rigid connection to the core structure to a minimum with adjacent the pivotal connection to the armature assembly, it is possible substantially uniformly to stress the respective fiexures, thus reducing their mass so as to minimize the reciproeating mass of the armature assembly.

In another specific aspect each pivotal connection comprises three springs or leaves of a flexible material. The opposite ends of the respective leaves are substantially rigidly attached to the armature assembly and correlated flexures. Two of the leaves of each connection are arranged in spaced relationship in a common plane and the third leaf interposed between the two leaves with its plane substantially normal to the plane thereof, whereby movement of the end of the flexure bends all three leaves conjointly so that the resultant action is essentially that of a pivotal connection.

Another feature of the invention is the possibility of positioning a generator of electrical signals upon the opposite side of the core structure from the air gap, thereby to shield the generator from the leakage flux and at the same time making it possible to connect the moving element of the generator directly to the test table so that the output signal is a function of the velocity of the test table itself rather than of some other element of the armature assembly which may have another mode of vibration.

These and other objects, aspects and features of the invention will be apparent from the following description of a specific embodiment of the invention which refers to drawings wherein:

Fig. 1 is a plan view of a vibrationgenerator;

Fig. 2 is a side elevation of the generator shown in Fig. 1

Fig. 3 is a sectional view on lines 3-3 of Fig. 1;

Fig. 4 is an enlarged fragmentary elevation View showing the details of construction of one column of the armature assembly;

Fig. 5 is a fragmentary sectional view on lines 5-5 of Fig. 4;

Fig. 6 is a section-a1 view similar to Fig. 5 illustrating an alternative construction;

Fig. 6a is a fragmentary detail view of the end of the column in Fig. 6;

Fig. '7 is an isometric view of one of the flexures located at the coil end of the armature assembly;

Fig. 8 is a side elevation view showing the action of the fiexure illustrated in Fig. 7; and

Fig. 9 is a fragmentary view of one of the flexures located at the table end of the armature assembly.

As is shown in Figs. 1 and 3, the vibration generator, chosen for purposes of illustration, comprises a substantially cylindrical core structure ID of a low reluctance magnetic material. The

core structure 10 is supported upon a base I! having two integral upright brackets I4 which are located. upon opposite sides of the base. At the top of each of the brackets I4 is provided a bearing surface wherein is journaled, respectively, one of the two oppositely disposed trunnions 16 which extend radially from the wall of the core structure ID. The trunnions [6 are maintained in contact with the bracket bearing surfaces by means of caps l8 which are bolted or otherwise secured to the respective brackets l6.

As is best shown in Fig. 3, the core structure I!) is provided with a deep annular recess 28 which is coaxially positioned with respect to the axis of the structure so that the core is separated into a central pole portion 22 and an outer ring portion 24. Acore magnetizing coil 26 of conventional design is supported in the recess 28 by means of a plurality of spacers 28 and an annular cover plate 38 which is secured to the bottom surface of the ring portion 24 of the core structure In by means of cap screws 32. With the cover plate 30 secured in place as described above, a magnetic path is completed which is essentially E-shaped in cross-section, thereby to form a cylindrical air gap 35 between the opposed cylindrical face of the extended end of the central pole portion 22 and the wall of the central aperture in the annular cover plate.

The armature assembly is designated generally by the numeral 48 and comprises a test table or bed 42 whereupon can be mounted test specimens or from which subsidiary mechanism or apparatus (not shown) can be driven. The table 42 is generally hexagonal in shape, as is shown in Fig. 1, and is provided with a skirt 44 (Fig. 1) at each of whose intersecting sides is provided a respective recessed boss 46 so that a rigid structure is formed with a minimum mass. As is best shown in Fig. 5, each of the bosses 4B is recessed from the bottom to provide a socket wherein is inserted the end of a respective hollow connecting member or column 48. The end of each of the columns 48, which is inserted in a respective boss aperture, is closed as at 49 except for a threaded hole for engaging a cap screw 50 which secures the column to the table 42. The top of the bosses 48 are also recessed So that the heads of the cap screws 58 are sunk well below the surface of the table 42, the recesses being threaded to provide a convenient means for attaching test specimens to the table.

The lower ends of the respective columns 48 are provided with axially extending slots having an offset in the bottom thereof wherein is inserted a cylindrical member or barrel 52 which acts as a spacer to maintain the columns in parallel relationship. The upper end of the barrel 52 is secured to each of the columns 48 by means of a flat-headed rivet 54 which also passes through internal spacers 56 and 58 positioned on either side of the barrel 52 within the column 48. It will be noted that, because of the ofiset of the lower portion of the slot, the spacers 5B and 58 are of different maximum thickness. The lower end of the barrel 52 is secured in a similar manner, but the spacer 6-0 is thinner than the corresponding upper spacer 56 so that a ring 62 can be inserted between the spacer 68 and the barrel 52.

The ring 62 is of a non-metallic material and has a lower portion which is of a greater width so that it is substantially of the same .width as the slot to form an integral lip which acts as an end ring for an armature coil 65. The coil 65 is not carried upon a spool but is wound upon a collapsible mandrel (not shown) of wire having sufiicient diameter whereby it is stifi enough so that the coil is self-supporting. The coil 65 is maintained in the wider portions of the slots in the columns 48 by means of a plurality of set screws 66. Each of the screws 66 is threaded, respectively, into the bottom of a correlated cylindrical block 69 which is held in the lower end of the corresponding column 48 by two opposed pins 68. The ends of the set screws 66 bear against the bottom of a lower end ring 10, thereby to compress the coil 65 between the lower ring 10 and the wider end of the upper end ring 82.

An alternative manner of securing the armature coil 65 is shown in Fig. 6 wherein the columns 48a are foreshortened and the slots for the barrel 52a have no ofiFset but are positioned so that the barrel passes through the axis of the columns. The upper end of the barrel 52a is secured to each of the columns .by a respective rivet 54 and spacers 56a and 58a in'a mannor-similar to that described in detail heretofore in connection with the embodiment shown in Fig. 5; The lower foreshortened end of the column 484: is necked down as at 49 and a rivet 54a passed therethrough to secure the lower end of the barrel 52a. The rivet 5411 also' passes through the separated portionsof a slotted end ring 52a for the coil 65. lihe lower end ring I0 is supported by a plurality of straps 12 which extend downwardly beyond the ends of the respective columns 48a. Each'of the straps 12 is bent around the lower end ring Hi so that its ends are adjacent either side of the slotted upper end ring 62m to'which the" strap ends are secured by two rivets 54b. These rivets also pass through the lower end of the barrel 52a which is insertedin the slot in the upper end ring 62a.- The coil 65 is compressed between the end rings 62a. and 18a by means of the set screws 66a (Fig. 6a), one of which is threaded into either side-of a respective'block (59a carried in the'bottom of each strap 12.

The armature assembly 40 is mounted in the core structure It by removing the tabled! and inserting the columns 48 (or 48a.) through equally-spaced apertures 14 and 16 provided in the core structure 22 and the cover plate 39, respectively, so as to connect with the recess 20 in the core structure Ill.

The armature assembly id is constrained so that it can move only in anaxial direction by means of two pairs of deflectable members or fiexures 80 located, respectively, at either end thereof. As is shown in Fig. 7, one end of each flexure 80 is rigidly attached by means of bolts 84 to a respective boss 82 which extends'from the. core structure. The two bottom flexures- Bil are electrically insulated from the bosses 82 by means of spacers 81 of a non-conducting ma terial which are positioned on either side of the flexures.

The opposite ends of the bottom fiexures 8%! are attached to the plastic lower coil end-ring by means of a-pivotal joint 85, which is shown in Figs. 'land 8- and will be described in detail hereinafter. As the bottom flexures are insulated from both the core structure lit-and metal portions of the armature assembly 40; the flexures can be used as electrical conductors for energizing the coil 65, thus eliminating loose wires and the resulting breakage. The upper flexures 80 are attached by similar pivotal joints 85a to arms 86 (Fig. 9) which extend respectively from two opposed columns #8.

As is shown in Figs. 7- and- 8, each of the pivotal joints 85 comprises two spaced spring leaves 88, one end of each of which is rigidly clamped between a rectangular washer 39 at the end of the flexure by means of a screw 98. The opposite ends of the leaves are rigidly clamped in a similar manner to the top of a T-shaped bracket 9-l whose other end is slotted to receive the coil'end ring 19 to which it is secured by a; screw 92-. Interposed between the spaced leaves 88, and normally disposed at right. anglesthereto,. is a third leaf 9 3 whose ends are rigidly clamped, respectively, by rectangular washers 94 and screws 95 to. the side of the 'T-shaped the ends clamped to the fiexures are clamped to the arm 86 rather than the T-shaped bracket 9|.

The operation of the above-described pivotal joints can best be understood by reference to Fig. 8 wherein the solid lines represent the normal unstressed position of the flexure 80. As the end ring 10 is moved upwardly to the position 10 indicated by the broken lines, the flexure is bent as is indicated at the leaves 88 and 94 bending simultaneously at the line of intersection of their planes, which line' is the equivalent of a pivot which moves without friction except for the internal bending strains in the leaves. From the above it will be apparent that with one end of each of the fiexures 80 rigidly secured and the opposite end each having a pivotal connection, the respective flexures each act as a cantilever beam. To reduce the stress concentration at the rigid support, each of the flexures is tapered in width towards its pivoted ends at a rate which reduces the width of the flexure so that the stress therein is substantially constant throughout its length. With a uniform stress,- the mass of the fiexure can be minimized, thereby further reducing the total reciprocating mass of the armature assembly 40 to permit maximum accelerations.

The velocity of the table 42 of armature assembly 43 is determined by means of the'output signal obtained from an armature coil 99 of a signal generator Hit. The coil is attached to the head at the lower end of a bracket I02. The other end of the bracket N32 is secured by means of a cap screw M4 in a socket located at the center of the table 42 so that the coil is disposed in the air gap of a generator stator. The stator comprises a portion I56 of a low reluctance material which is held in arecess in the end of the central portion 22 of the core structure it by means of a screw [08 which also passes through the end and spool pieces H0 and H2 comprising the remainder of the magnetic pathof the stator. The spool piece H2- is apermanent'magnet producing a constant magnetic flux in the air gap so that as the coil 99 is moved by the armature assembly 40, a voltage is induced in the coil which is a. function of the velocity of the coil 99 and therefore of the table 412 to which it is attached.

The above-described vibration generator is energized by supplying a direct current to the field coil 26. When an alternating current is supplied to the armature coil 65, the armature assembly 40 is caused to reciprocate at a frequency determined by tho frequency of the alternating current so that controlling the frequency of the coil current controls the reciprocating rate of the test table 42.

It should be understood that the present'di'sclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

We claim:

1. A vibration generator comprising a core structure having an air gap, coil means for magnetizing the structure to introduce a high flux concentration across said gap, an armature assembly carrying a table at onev end thereof so that the table is positioned without said core structure upon the opposite side thereof from said gap, said assembly also including arr electrical coil in said air gap and a plurality of spaced: elongamd connecting members disposed about the: peripheryof said table and; extending.

through said core structure to support said coil, and flexure means extending between said structure and said assembly for limiting the travel of said assembly so that the coil is constrained to move axially without lateral contact with the core structure.

2. A vibration generator comprising a cylindrical core structure having an axial cross-section which is essentially E-shaped forming a cylindrical air gap at one end thereof, said structure having a plurality of equally spaced apertures extending therethrough at equal distances from the structure axis, a field coil disposed about the central leg of the core structure for magnetizing the structure to introduce a high flux concentration across said gap, an armature assembly carrying a table at one end thereof so that the table is positioned without said core structure upon the opposite end thereof from said gap, said assembly also including an armature coil located in said air gap and a plurality of elongated connecting members disposed about the periphery of said table and extending through respective apertures in said core structure to support said armature coil, and flexure means extending between said structure and said assembly for limiting the travel of said assembly so that the coil is constrained to move axially without lateral contact with the core structure.

3. A vibration generator comprising a core structure having an air gap at one end thereof, said structure having a plurality of equally spaced apertures extending therethrough at equal distances from the structure axis; a field coil for magnetizing the core structure to introduce a high flux concentration across said gap; an armature assembly carrying a table at one end thereof so that the table is positioned without said core structure upon the opposite end thereof from said gap, said assembly also including an armature coil located in said air gap, a plurality of elongated connecting members disposed about the periphery of said table and extending through respective apertures in said core structure, a spacer attached to the opposite end of the connectin members to maintain the relative position of the members, and attaching means for securing the armature coil to the spacer; and flexure means extending between said structure and said assembly for limiting the travel of said assembly so that the coil is constrained to move axially without lateral contact with the core structure.

4. A vibration generator comprising a core structure having a cylindrical air gap at one end thereof, said structure having a plurality of equally spaced apertures extending therethrough at equal distances from the structure axis; a field coil for magnetizing the core structure to introduce a high flux concentration across said gap; an armature assembly carrying a table at one end thereof so that the table is positioned without said core structure upon the opposite end thereof from said gap, said assembly also including an armature coil located in said air gap and a plurality of elongated connecting members disposed about the periphery of said table and extending through respective apertures in said core structure, a cylindrical member attached to the extending ends of the connecting members to act as a spacer therefor to maintain the relative position of the connecting members, and a plurality of straps encircling the armature coil to secure the armature coil to the outwardly ex tending end of the cylindrical member; and two pairs of spaced flexures extending between said structure and said assembly for limiting the travel of said assembly so that the coil is constrained to move axially without lateral contact with the core structure, one pair of flexures extending between the table and the core structure, the other pair of flexures extending between the external end of the coil and the core structure.

5. A vibration generator comprising a core structure having an air gap at one end thereof, said structure having a plurality of equally spaced apertures extending therethrough at equal dis tances from the structure axis; a field coil for magnetizing the core structure to introduce a high flux concentration across said gap an armature assembly carrying a table at one end thereof so that the table is positioned without said core structure upon the opposite end thereof from said gap, said assembly also including an armature coil located in said air gap and a plurality of elongated connecting members disposed about the periphery of said table and extending through respective apertures in said core structure, the extending ends of the respective connecting members having axially disposed slots therein, a cylindrical member secured in the slots in the connecting members to act as a spacer therefor to maintain the relative position of the connecting members, and a plurality of straps encircling the armature coil to secure the armature coil to the outwardly extending end of the cylindrical member; and flexure means extending between said structure and said assembly for limiting the travel of said assembly so that the coil is constrained to move axially without lateral contact with the core structure.

6 A vibration generator comprising a core structure having an air gap at one end thereof, said structure having a plurality of equally spaced apertures extending therethrough at equal distances from the structure axis; a field coil for magnetizing the core structure to introduce a high flux concentration across said gap; an armature assembly carrying a table at one end thereof so that the table is positioned without said core structure upon the opposite end thereof from said gap, said assembly also including an armature coil located in said air gap and a plurality of elongated connecting members disposed about the periphery of said table and extending through respective apertures in said core structure, said extending ends of the respective connecting members having axially disposed slots, a cylindrical member secured in the bottom of the slots in the connecting members to act as a spacer therefor to maintain the relative position of the connecting members, the armature coil being secured in the slots over the cylindrical member; and flexure means extending between said structure and said assembly for limiting the travel of said assembly so that the coil is constrained to move axially without lateral contact with the core structure.

'7. A vibration generator comprising a core structure having an air gap, coil means for magnetizing the core structure to introduce a high flux concentration across said gap, an armature assembly carrying a table at one end thereof so that the table is positioned without said core structure upon the opposite side thereof from said gap, said assembly also including an electrical coil located in said air gap and a plurality of elongated connecting members attached to said table and extending through said core structure to support said coil, and two pairs of spaced flex- 9 ures' located, respectively, adjacent the opposite ends of the core structure and extending between said structure and said assembly for limiting the travel of said assembly so that the coil iscor i-' strained to move axially without iateral contact with the core structure.

8. A vibration generator comprising a core structure having an air gap at one end thereof, said structure having a plurality of equally spaced apertures extending therethrough at equal distances from the structure axis; a field coil for magnetizing the core structure to introduce a high flux concentration across said gap an armature assembly carrying a table at one end thereof so that the table is positioned without said core structure upon the opposite end thereof from said gap, said assembly also including anarmature coil located said gap and aplurality of elongatedconnecti ng members disposed about the periphery of said table and extending through respective apertures in said core structure, a cylindrical member attached to the opposite end of the connecting members to act as a spacer therefor to maintain the relative position of the connecting members, and a plurality of straps encircling the armature coil to secure the armature coil to the outwardly extending end of the cylindrical member; and two pairs of flexures for limiting the travel of said assembly so that the coil is constrained to move axially without lateral contact with the core structure, one pair of flexures extending between the table and the core structure, the other pair of flexures extending between the external end of the coil and the core structure.

9. A vibration generator comprising a core structure having an air gap, coil means for magnetizing the core structure to introduce a high flux concentration across said gap, an armature assembly carrying a table at one end thereof so that the table is positioned Without said core structure upon the opposite side thereof from said gap, said assembly also including an electrical coil located in said air gap and a plurality of elongated connecting members attached to said table and extending through said core structure to support said coil, and two pairs of fiexures located, respectively, adjacent the opposite ends of the core structure and extending between said structure and said assembly for limiting the travel of said assembly so that the coil remains in said air gap, the respective connections between the core structure and each of the flexures being substantially rigid, the respective connec tions to the armature assembly being pivotally arranged so that the flexures act essentially as cantilevers.

10. A vibration generator according to claim 9 wherein the thickness of the flexure in the direction of movement of the armature assembly is relatively small with respect to its width in a transverse direction to said movement.

11. A vibration generator according to claim 10 wherein the transverse width of each fiexure is gradually decreased from a maximum width adjacent the rigid connection at the core structure to a minimum width adjacent the pivotal connection at the armature assembly, the rate of taper being such that the stress in the fiexure is substantially uniform.

12. A vibration generator comprising a core structure having an air gap, coil means for magnetizing the core structure to introduce a high flux concentration across said gap, an armature assembly carrying a table at one end thereof so that the table is positioned without said core structure upon the opposite side thereof from said gap, said assembly also including an electrical coil located in said air gap and a plurality ofelongated connecting members attached to said table and extending'through said core struc ture to support said coil, and two pairs of flex ures'located, respectively, adjacent the opposite" ends of the core structure and extending between said structure and said assembly for limiting the travel of said assembly so that the coil is com strained to move axially without lateral contactwitli the core structure, the respective con-nee tions between the core structure and each or the flexures being. substantially rigid,- the respective connections to the armature assembly beingpie-'- otall y' arranged so that the fiexur'es act essentially as cantilevers, each pivotal connection including two leaves of flexible material, the opposite ends of which are substantially rigidly attached to the armature assembly and correlated flexure respectively, the planes of the leaves being disposed at approximately right angles.

13. A vibration generator comprising a core structure having an air gap, coil means for magnetizing the core structure to introduce a high flux concentration across said gap, an armature assembly carrying a table at one end thereof so that the table is positioned without said core structure upon the opposite side thereof from said gap, said assembly also including an electrical coil located in said air gap, and a plurality of elongated connecting members attached to said table and extending through said core structure to support said coil, and two pairs of flexures located, respectively, adjacent the opposite ends of the core structure and extending between said structure and said assembly for limiting the travel of said assembly so that the coil is constrained to move axially without lateral contact with the core structure, the respective connections between the core structure and each of the flexures being substantially rigid, the respective connections to the armature assembly being pivotally arranged so that the flexures act essentially as cantilevers, each pivotal connection including two spaced leaves of flexible material and a third leaf positioned between the first two leaves with its plane substantially normal to the plane thereof, the opposite ends of all three leaves of each connection being substantially rigidly attached to the armature assembly and correlated flexure, respectively.

14. A vibration generator comprising a core structure having an air gap, coil means for magnetizing the core structure to introduce a high flux concentration across said gap, an armature assembly carrying a table at one end thereof so that the table is positioned without. said core structure upon the opposite side thereof from said gap, said assembly also including an electrical coil located in said air gap and a plurality of equally spaced elongated connecting members disposed about the periphery of said table and extending through said core structure to support said coil, 2. generator of electrical signals which are a function of the table velocity interposed between said table and said core structure where said generator is shielded by said structure from leakage flux from said gap, and flexure means extending between said structure and said assembly for limiting the travel of said assembly so that the coil is constrained to move axially without lateral contact with the core structure.

15. A vibration generator comprising a core structure having an air gap, coil means for ma netizing the core structure to introduce a high flux concentration across said gap, an armature assembly carrying a table at one end thereof so that the table is positioned without said core structure upon the opposite side thereof from said gap, said assembly also including an electrical coil located in said air gap and a plurality of equally spaced elongated connecting members disposed about the periphery of said table and extending through said core structure to support said coil, a generator of electrical signals which are a function of the table velocity interposed between the core structure and table where the generator is shielded from the leakage flux from said gap, said generator including a magnetized core member having a gap and a coil member, one of said members being attached to said core structure and the other member being attached PHILIP C. EFROMSON. ROBERT C. LEWIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,808,149 Smith June 2, 1931 2,128,722 Wickersham Aug. 30, 1938 2,134,064 Ulrich et a1 Oct. 25, 1938 

